Bioactive materials for killing or inhibiting the growth and/or proliferation/spreading of bacteria, fungi, and other microorganisms have long been sought and employed in society. Their use dates back centuries, if not thousands of years. Early applications had ranged from pharmaceutical or health related applications to disinfectant and purification applications and more. More recent applications include a whole host of uses, with the largest use, by volume, seen in the agricultural industry. Perhaps one of the earliest bioactive materials was metallic silver and, subsequently, silver salts.
While early bioactive agents were most often metals and simple metal salts, modern science and chemical synthesis have enabled the development and production of synthetic agents, most often organic and organometallic agents, for antibacterial, antifungal and other like applications. Indeed, for many applications, especially pharmaceutical applications, the organic agents have, for the most part, eclipsed the use of inorganic bioactive agents. While inorganic and organometallic materials still command a significant market share of the agrichemical business, their use is limited due to their health and safety concerns, especially from an environment perspective. Indeed, organic bioactive agents command a huge portion of the agrochemical business.
Despite the great success and huge market share/volume commanded by organic pharmaceutical, antibacterial and agrochemical agents, they have not come without cost and consequences. In all areas of applications, a marked and growing trend has emerged: namely the manifestation and spreading of a resistance to such organic agents in most all, if not all, microorganisms. While this resistance is neither universal nor complete, it is growing and involves more and more organic agents. As their resistance grows, so too does their apparent virulence. In this respect, we are all well aware of the growing resistance of bacteria, especially pathogenic bacteria, to traditional pharmaceutical antibiotic agents and the subsequent appearance of what are commonly referred to as superbugs: pathogenic bacteria that show strong resistance to traditional organic antibacterial and pharmaceutical agents.
And, whether a direct or indirect consequence of the appearance of superbugs and/or the growing awareness of the ease by which bacteria can spread combined with an increasing concern for potentially pandemic diseases such as SARS and Bird Flu, we have become a population that is more and more pre-occupied with hygiene and general cleanliness. Consequently, there has been a huge proliferation and exponential growth in the widespread and indiscriminate use and application of cleansers and disinfectants that contain organic antimicrobial agents, all in an effort to ward off exposure to bacteria and, especially, superbugs. However, this indiscriminate use of organic agents has come with, or at least presents the possibility for, an overall increase in antimicrobial resistant organisms. By eradicating the weaker organisms, the stronger and, most often more damaging, organisms are left.
A similar consequence has manifested itself in the agricultural industry as well, especially in that portion relating to crop/food production. The widespread and repetitive use of organic biocides, fungicides, antibacterial agents and the like, has led to the manifestation of less and less efficacy of the same against the targeted diseases: an indicator of a growing resistance. Perhaps more alarming is the speed with which such resistance has begun to appear. For example, despite the great fanfare and promise behind the introduction of strobilurin fungicides in the mid-1990s, resistance had been found after just a couple years use in certain applications. Such a growing trend bodes ill for an industry where fewer and fewer acres are called upon to produce more and more crops to feed the ever growing populations while those organisms and microorganisms responsible for attacking such crops become stronger and stronger and more and more resistant to traditional control means.
While resistance is certainly of great concern, perhaps and even greater concern is the human and environmental toll associated with the widespread use of organic antimicrobial agents. For more than half a century now, more and more scientific literature has appeared correlating long-term exposure (direct and indirect) and use of such organic agrichemicals to various diseases and teratogenic, mutanogenic, and other adverse health consequences in animals and, more importantly, the human population. Perhaps the watershed of this awareness is represented by the outcry relating to the use of DDT and like pesticide agents in the 1960s. In humans, such a correlation of birth defects, cancer, and other diseases with organic agrichemicals is especially disconcerting for those whose water supplies have or may become contaminated with such organic agents due to their and/or their by-product's solubility and long half-lives. Of course drinking water is only one exposure source: another exposure source concern is inhalation from dust blown up from the fields, from wayward aerosols and/or particulates during aerial spraying and dusting, respectively, and from exposure to the clothing of workers who, themselves, were exposed in the fields or during application.
In an effort to move away form organic agents, more recent attention has once again focused on the inorganic agents, including organometallic agents, since these tend to show or have no, or certainly less, tendency to result in resistant bacteria, fungi and the like. However, such a trend merely reawakens the debates and concerns relative to the large-scale dumping of heavy metals in the environment. Although some efforts have recently focused on improving the old, traditional inorganic agents, much more effort, particularly in the non-agricultural arena, has seemingly focused on more complex species and systems, in essence, synthesized inorganic biocides such as the antimicrobial ion-exchange type antimicrobial agents based on zeolites, hydroxy apatite, and zirconium phosphates. Other recent biocides include those based on electrolytically generated silver citrates; thiol-free, specialty complexes of antimicrobial metals; sulfuric acid/sulfate complexes prepared under high pressure and temperature; and the like. While effective, these have limited applications and entail added costs owing to the complex and/or lengthy synthetic processes by which they are prepared. The latter is of especial concern in the agricultural industry where the relative cost to performance trade-off oftentimes precludes the use of functionally very viable options. Here, a few cents per acre difference, even a fraction of a cent difference per acre, can mean the world of difference in the acceptability and utility of a given agent.
Despite their inherent environmental and health concerns, the use of “natural” inorganic agents, including manufactured/processed inorganic agents, has been pushed more and more by various environmental and conservation groups, as well as health advocates, as a favorable replacement to organic agents. While such pressure alone is not likely to change the industry, the growing resistance to organic agents combined with the higher and higher costs of synthetic organic agents, is certainly having an impact: not only in the agricultural industry but across the board in all applications for such bioactive agents. However, as noted above, the reintroduction of and/or increased use of inorganic agents merely brings to the forefront the very issues that caused them to be pushed back to begin with, namely environmental toxicity and contamination and bioaccumulation. Concern is not just for the effects during application, but more so for the long term effects associated with the continual build-up of these inorganic agents or their derivatives, especially the metals, in the environment and in living organisms. Such build-up not only pertains to the soils that are treated but also underground water supplies that may be replenished from the treated fields. Concern also exists, sometimes more so, for the consequences of rain-water run-off carrying the metals into local streams and, again, downstream water supplies. Ultimately, this build-up also occurs in the food chain, with higher and higher concentrations being found in those species in the higher order of the food chain. Ultimately, this affects the human supply chain as seen, for example with mercury and other metals in tuna and swordfish. While many metals, at least at low exposure levels, have little or no affect on humans, their impact is far greater on marine and other aquatic life, especially fish, which tend to be extremely sensitive to heavy metals, like silver, resulting in increase stress and, in extreme exposure situations, widespread kills.
Consequently, as part of this resurgence of inorganic bioactive agents, there has been a significant increase in research and development dollars and time spent to address concerns relative to the use of such inorganic agents. A prime focus has been with respect to making more concentrated materials that, it is hoped, will enable the use of less overall materials. In the agrichemical arena, one of the inorganic agents receiving the greatest attention, owing to its high efficacy, is copper. Indeed, it is thought that copper could see a manifold increase in use as organic agents are either precluded from use or farmers opt out for more natural agents. According to NCFAP data, in 1997 more than 13.7 million pounds of copper was used in fungicide applications as compared to 40 million pounds of synthetic fungicides at a treatment rate of about one-half that of copper. If all synthetic fungicides were to have been supplanted by copper, it would have resulted in an increase of more than 80 million pounds of copper released into the environment. Now, ten years later, though data is not available, one can only assume the amounts are much higher. Furthermore, this is but one use of copper: copper and copper based bioactive compositions are also used in other areas such as algaecides, etc. Regardless, it is clear that any significant shift from synthetic to copper fungicides, algaecides, etc. means a huge impact and release of copper into the environment.
As noted above, recent R&D efforts with inorganic fungicides have focused on the development of improved inorganic agents that produce better effects with less application. Indeed, in August 2006, DuPont, one of the leading manufacturers of agrichemicals, especially copper based fungicides, announced certain breakthroughs, as they described them, in copper fungicides, specifically its Kocide 3000 copper hydroxide based fungicide, touting their ability to provide more antifungal action with less copper. Still, its typical application rate is on the order of 1650 grams of copper per acre per application, with somewhat lower rates, 330 grams per acre, allowed for certain applications. While certainly an improvement over conventional or traditional copper based fungicides which are applied at nearly 4.5 pounds per acre, it still means the intentional release of huge amounts of copper into the environment, even more if the environmentalists are successful in removing or banning the use of more and more organic agents.
Thus, there is still a tremendous need for cost effective, inorganic agrichemical agents that provide good antimicrobial, antifungal, antibacterial, etc., activity without concern for resistance build-up.
In following, there is a need for inorganic antimicrobial, antifungal, antibacterial, etc., agents that may be used universally, or nearly so, without concern, or certainly with reduced concern for environmental contamination and toxicity, especially less so than exists with current inorganic agents.
Similarly, there is a need for inorganic agents that are stable and easy to use, and provide good short term and, preferably, longer term efficacy as compared to many of the current short lived organic agents.
Additionally, there is a need for such inorganic agents that can safely be use in agricultural and horticultural applications, including soil and seed treatment, crop/food producing plants and trees, ornamental and flowing plants and tress, fee and ornamental grasses, and the like with minimal exposure concerns.
Furthermore, there is a need for inorganic bioactive agents that can be use in combination with conventional inorganic and, preferably, organic agrichemical actives and compositions, especially, antimicrobial, antifungal, antibacterial, antiprotist, etc. agents with synergistic results; thus, enabling less use, overall, of such actives.
Finally, there is a need for bioactive agents that provide efficacious antimicrobial, antifungal, antiprotist, and/or antibacterial performance with minimal release of inorganic metals to the environment.